1. Field of the Invention
The present invention relates to an organic light emitting device and method of manufacturing the same, and more particularly, to an organic light emitting device with improved emission efficiency and/or service life.
2. Discussion of the Related Art
To date, liquid crystal display (LCD) devices are being widely used as flat panel display devices. LCD devices use a backlight as a separate light source, and have technical limitations in brightness and contrast. On the other hand, since organic light emitting devices self-emit light, organic light emitting devices do not need a separate light source and have relatively better brightness, contrast, and viewing angle, and thus, interest in organic light emitting devices is increasing. Also, since organic light emitting devices do not use a backlight, organic light emitting devices can be manufactured to be thin and lightweight, and have low power consumption and fast response time.
Organic light emitting devices are categorized into a top emission type, a bottom emission type, and a dual emission type depending on emission direction of light. Organic light emitting devices are categorized into passive matrix organic light emitting devices and active matrix organic light emitting devices depending on driving mode.
FIG. 1 is a diagram illustrating a red, green, and blue pixel structure of an organic light emitting device having a micro-cavity structure according to the related art. FIG. 1 illustrates a pixel structure of an active matrix organic light emitting device having a top emission type.
Referring to FIG. 1, the organic light emitting device includes an anode electrode 10, a cathode electrode 70, and an organic emission layer. The organic light emitting device according to the related art has a structure in which the organic emission layer is formed between the cathode electrode 70 injecting electrons and the anode electrode 10 injecting positive holes. A capping layer (CPL) 80 is formed on the cathode electrode 70.
The anode electrode 10 is formed as a reflective electrode, and the cathode electrode 70 is formed as a semi-transmissive electrode, thereby forming a micro-cavity structure. An optical cavity is formed between the cathode electrode 70 and the anode electrode 10. The cathode electrode 70 transmits some (e.g., 60%) of the light emitted from the organic emission layer, and the remaining light (e.g., 40%), which is not transmitted, is reflected to cause constructive interference suitable for each wavelength, thereby enhancing emission efficiency.
The organic emission layer includes a hole injection layer (HIL) 20, a hole transport layer (HTL) 30, a plurality of emission layers (EMLs) 52, 54 and 56, an electron injection layer (EIL, not shown), and an electron transport layer (ETL) 60. In this case, the electron injection layer (EIL) may be omitted.
One unit pixel includes a red pixel Rp, a green pixel Gp and a blue pixel Bp of three colors. The organic emission layer of the red pixel further includes a red HTL 42. The organic emission layer of the green pixel further includes a green HTL 44.
The red emission layer 52 of the red pixel Rp is formed between the ETL 60 and the red HTL 42. The green emission layer 54 of the green pixel Gp is formed between the ETL 60 and the green HTL 44. The blue emission layer 56 of the blue pixel Bp is formed between the ETL 60 and the HTL 30.
When electrons generated from the cathode electrode 70 and holes generated from the anode electrode 10 are injected into the EMLs 52, 54 and 56, the injected electrons and holes are recombined to generate excitons. The generated excitons are shifted from an excited state to a lower-energy state to emit red light, green light, and blue light from the red EML 52, the green EML 54, and the blue EML 56, respectively.
Due to an emission structure and a material of the emission layer, the organic light emitting device according to the related may have limitations in emission characteristic and performance of service life.
To address such a limitation, a method has been proposed in which emission efficiency is enhanced by changing a fluorescent material to a phosphor material for the emission layers 52, 54 and 56. However, this method may also have a problem in that more power is consumed as luminance increases, and moreover, emission efficiency may become lowered when the light emitting material is changed for securing a long service life.
As the resolution of display devices advances to a high resolution, the number of pixels per unit area increases, and high luminance is needed. However, due to an emission structure of the organic light emitting device according to the related art, the luminance of the unit area may be limited, and due to increase in an applied current, the reliability of the organic light emitting device may be degraded, and the power consumption may increase.
Moreover, among pixels of three colors of the organic light emitting device, the blue pixel may have a shorter service life than those of the red and green pixels, and thus, the service life of the organic light emitting device may not be ensured.